A constellation is a pattern formed by prominent stars within apparent proximity to one another in Earth's nighttime sky. The zodiac is the ring of constellations that the Sun seems to pass through each year as the Earth orbits around it. While there are actually thirteen zodiacal constellations, the following twelve constellations comprise the twelve signs of the modern zodiac: Capricorn, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, and Sagittarius. Each of these twelve signs corresponds to the Gregorian dates during which the Sun passes through a sign in the Ptolemaic tropical zodiac, as shown in Table I, below.
TABLE ISignDatesCapricornDecember 22 to January 20AquariusJanuary 20 to February 18PiscesFebruary 18 to March 20AriesMarch 20 to April 20TaurusApril 20 to May 21GeminiMay 21 to June 21CancerJune 21 to July 23LeoJuly 23 to August 23VirgoAugust 23 to September 23LibraSeptember 23 to October 23ScorpioOctober 23 to November 22SagittariusNovember 22 to December 22
One's date of birth determines which sign one is according to the dates in Table I, above. The twelve signs of the zodiac are used in various applications, such as astrology, which is the study of correlations of celestial events with behavior on earth.